Transmission gear ratio selection

Abstract

An objective method is provided for selecting gear ratios for use in a motor vehicle transmission having multiple selectable gears. The method includes selecting gear ratios for a specific application includes calculating a low gear ratio, and a high gear ratio based upon vehicle parameters and performance requirements. The total ratio spread is determined by dividing the low gear ratio by the high gear ratio. Using the total ratio spread, a geometric sequence is created with a plurality of terms, such that each of the terms respectively represent the ratio steps between the gears. Lastly, each gear ratio is divided by its respective ratio step plus one to find the gear ratio for the next gear. This method provides an objective method for selecting gear ratios, such that the steps between each of the ratios are uniformly progressive.

What is claimed is:  
     
       1. A method of selecting gear ratios for use in a motor vehicle transmission having a plurality of gears ranging between a low gear and a high gear, which comprises: 
       determining a low gear ratio for the low gear, and a high gear ratio for the high gear;  
       determining a total ratio spread by dividing said low gear ratio by said high gear ratio;  
       determining a number of gear ratios;  
       determining a number of ratio steps by subtracting one from said number of gear ratios;  
       determining a ratio variable by raising said total ratio spread to a power inverse of said number of ratio steps;  
       determining values for said ratio steps by creating a geometric sequence having a plurality of terms representing each of said respective ratio steps such that a ratio of any two consecutive ratio steps is a common percent constant; and  
       successively determining a gear ratio for each gear in the transmission between the low gear and the high gear by dividing a gear ratio previously determined for a next lower gear by a ratio step plus one for the next lower gear so as to have uniformly progressive ratio steps, wherein narrow step ratios provide for a smaller skip shift index and wide step ratios provide for a larger skip shift index.  
     
     
       2. The method of selecting gear ratios as recited in  claim 1 , wherein said step of creating the geometric sequence further comprises determining values for each of said plurality of terms by raising said ratio variable minus one to different powers, such that a step ratio constant exists between each adjacent term of said plurality of terms. 
     
     
       3. The method of selecting gear ratios as recited in  claim 1 , wherein said step of creating the geometric sequence further comprises determining values for each of said plurality of terms by raising said ratio variable minus one to different powers, such that said plurality of terms create a geometric sequence.